SOI is a semiconductor technology that produces higher performing, lower power (dynamic) devices as compared to traditional bulk silicon-based technology. SOI functions by placing a thin, dielectric (electrically insulating) layer, such as silicon oxide or glass, between a thin top layer of a semiconductor material such as silicon and a supporting handle portion that is generally a silicon substrate.
Power integrated circuits (ICs) have gained importance due to their advantages of small size, low cost, lower power consumption, and increased reliability. Power ICs operating in the low to medium voltage range (e.g., 30 V to 120 V) are used in applications such as automotive electronics, light-emitting diode drivers, plasma display panels, PC peripheral, and portable power management products. Low ON-resistance is often achieved through a reduced surface field (RESURF) structure in the LDMOS device design. The RESURF structure is designed to deplete the drift space of the LDMOS device in both vertical and lateral directions, thereby reducing the electric field near the surface at the drift region and thus raising the OFF-state breakdown voltage (BVdss) of the device.
SOI is known for power ICs such as LDMOS devices because SOI provides superior electrical isolation between various devices on the chip as well as better performance. In an LDMOS device, the drain is laterally arranged to allow current to laterally flow, and a drift region is interposed between the channel and the drain to provide a high drain to source BV. LDMOS devices are thus generally designed to achieve higher BV while minimizing specific ON-resistance in order to reduce conduction power losses.
The specific on-resistance (RON) is defined as the product of total ON-resistance and area of the device. Both the voltage breakdown voltage (VBR) and the ON-resistance of SOI LDMOS are dependent on the length and doping of the drift region. A long drift region length and low doping is generally needed to achieve high breakdown voltage in a conventional LDMOS device, which unfortunately, increases the ON-resistance of the device. Conversely, a shorter drift region length with higher a doping level reduces the ON-resistance, but adversely affects the breakdown voltage. Therefore, there is generally always a trade-off between the breakdown voltage and the ON-resistance.